This invention relates to foamed fluids to be introduced into wellbores drilled into the earth for the production of hydrocarbons, to clean and stimulate the subterranean strata adjacent the wellbore. More specifically, it is concerned with a liquid composition and method of use of this liquid composition for producing foamed stimulation fluids for use in connection with wellbore cleanout, acidizing and hydraulic fracturing for purposes of workover or stimulation of injection or production wells.
In the drilling and subsequent maintenance of injection and production wellbores for the production of hydrocarbons from subterranean strata, it is often necessary to remove plugging materials from the face of the wellbore and from the subterranean strata near the wellbore. As is commonly known in the art, one method of accomplishing the removal of these plugging materials is to wash the wellbore and near-wellbore area in the subterranean strata with an acid to dissolve and/or loosen these plugging materials and improve near-wellbore subterranean strata permeability.
It is known that this "acidizing" of a wellbore can be made more effective by using a mixture of from about 70 to about 24 volume percent of a mixture of an octyl alcohol and a lower aliphatic alcohol selected from the group consisting of ethanol, the propyl alcohols and tertiary butyl alcohol and from about 30 to about 76 volume percent of an aqueous solution of a well acidizing, nonoxidizing, water-soluble acid (see U.S. Pat. No. 3,819,520). It has been shown that the alcohol mixture serves to reduce the interfacial tension between the acid and oil underground, thereby improving the displacement of oil by the acid.
It is known that when fluids are introduced into a wellbore, fluid loss to the subterranean strata surrounding the wellbore can be a significant problem. It is also known that foams have a number of advantages when employed in oilfield applications, including generally lower fluid loss. U.S. Pat. No. 4,217,231, recognizes the advantages of foams and teaches the use of small amounts (between 0.0005 to 0.05 weight percent) of an additive comprising certain alcohols and organic acids (those with between 5 and 10 carbon atoms) malonic acid and lower n-alkyl diesters of malonic acid in aqueous foams to further reduce fluid loss. This patent further recites that those alcohols with less than five carbon atoms act as foam breakers and that those alcohols with from 5 to 10 carbon atoms were widely believed to be defoamers but that in low concentrations (i.e., between about 0.005 to 0.05 volume percent) and especially at elevated pressures (greater than 500 psi, these additives are compatible with foam.
Thus, it is known that the acidizing of wellbores to remove and/or loosen plugging materials from the wellbore and the subterranean strata near the wellbore can be made more effective through the addition of a mixture of certain suitable alcohols to a suitable acid. It is also known that the use of foams in maintenance operations on oil and gas wells has a number of advantages, such as reduced stimulation fluid loss to the subterranean strata, improved ability of the stimulation fluid to lift and suspend fine solids from the wellbore and the subterranean strata adjacent the wellbore, reduced stimulation fluid volume requirements, reduced hydrostatic pressure at the bottom of the wellbore caused by the weight of the column of stimulation fluid in the wellbore and improved flowback of stimulation fluid, dissolved plugging materials and fine solids. Accordingly, there is a substantial and unfulfilled need to produce better foamed stimulation fluids comprising a suitable acid and a mixture of certain suitable alcohols so as to obtain the benefits associated with the use of a suitable acid and a mixture of suitable alcohols and the benefits associated with the use of foams in the maintenance of oil and gas wells.